A complete and utter moron. One who constantly blacks out, forgets important things and subsequently argues their point to be valid when everyone in the room knows it's not. A muk also enjoys looking at the sky while speaking.

that guy that when you see him your like "what a piece of shit", and when you see him you have to yell "M.U.K.!" but in a way that sounds like your throwing up
also that guy that no one wants to talk to or be around and that gets bricks thrown through his car window